The following practical data make the problem clear.
A top power concentration 1600 cc, naturally aspirated, mass production engine with four cylinders, 16 valves, 33 mm intake valve diameter and 29 mm exhaust valve diameter, has been modified according the VVA described in the PCT/GR04/000043, which is the closest prior art. Details of the modification are presented in the www.pattakon.com web site. The resulting engine provides flat torque throughout the entire power band with peak power at 9000 rpm and 12 mm intake valve lift. The engine has no throttle valve and when the intake valve lift is decreased to 0.15 mm it idles at 300 rpm. The flow during idling, i.e. 300 rpm with ⅙ of the full charge, is 180 times lower than the flow at 9000 rpm and full load. Assuming that an intake valve lift deviation of 0.02 mm is practicable, the maximum from minimum difference of the valve area, i.e. of the surface or restriction through which the mixture is sucked into the cylinder, at 12 mm valve lift is 1−[(12+0.02)/(12−0.02)] or 0.33%, at 10 mm valve lift it becomes 0.4%, at 4 mm valve lift it becomes 1%, at 2 mm valve lift it becomes 2%, at 1 mm valve lift it becomes 4% and at 0.15 mm valve lift, i.e. at idling, the maximum from minimum difference of the valve area becomes 31%. This means that during idling the quantity of mixture sucked into a cylinder could differ more than 30% from the quantity of mixture sucked into its neighbor cylinder.
The periphery of each intake valve is 33*π=103.6 mm, the periphery of the two intake valves is 2*103.6=207.2 mm, the idling lift is 0.15 mm, the total valve area is 0.15*207.2=31 mm2, so the valve area of the two intake valves is equivalent to a hole of 6.29 mm diameter. The ratio 207.2/0.15, i.e. the total periphery of the two intake valves to the idling valve lift, equals to 1381. To control the area of a rectangle with sides 207.2 mm and 0.15 mm by changing only the tiny 0.15 mm side, is difficult and vulnerable: a deviation of 0.02 mm on the 0.15 mm side of the rectangle results in a 30% maximum to minimum difference of rectangle's area while the same deviation on the 6.29 mm diameter of the equivalent hole results in only 1% difference of maximum to minimum hole's area.
The problem is not of the specific VVA. It is general for all throttle-less VVAs: whilst at the one moment the intake valves must perform at high revs a highly stressed, long stroke motion for high power output, the next moment the same intake valves must perform a tiny stroke of extreme accuracy for idling.
In the patent applications US 20050172932, US 20050241598 and US 0050247278 some ways to bypass the problem are disclosed.